In general, vehicular air conditioning devices use the engine-driven compressor. However, if a vehicle has an idling stop function that automatically stops the engine under a predetermined idling stop condition like waiting at a traffic light, etc., when the vehicle has stopped idling, the engine-driven compressor also stops operating. Consequently, the air conditioning device becomes incapable of cooling when idling stops.
To deal with this problem, a motor-driven compressor may be provided in parallel with the engine-driven compressor in a refrigerant circuit as disclosed in Patent Document 1. In such configuration, the engine-driven compressor is used when the engine is operating, whereas the motor-driven compressor is used when the engine stops (when idling stops).